Apparatus for fractionating liquids



April 18, 1933. P. E. Kul-n. 1,904,144

APPARATUS FOR FRACTIONATING LIQUIDS Filed Jan. 25, 1930 INVENTORATTORNEY PAUL E. KUHL, F ELIZABETH, NEW JERSEY, ASSIGNOR TO STANDARD OILDEVELOP- Patented Apr. 18, 1933 UNITED STATES PATENT OFFICE KENTCOMPANY, A CORPORATION OF DELAWARE APPABATIIS FOR IRAGTIONATING LIQUIDSApplication filed January 25, 1930. Serial No. 423,367:

This invention relates to improvements in fractionating equipment andparticularly to means for controlling the side stream leaving thefractionating column.

In the operation of fractionating towers usually several side streamsare taken out besides the overhead product and the bottoms. The sidestreams consist of hot liquid collected on one or several plates of abubble tower, or in a pan, and are preferably passed through a str ppingcolumn before entering the final cooler. In this column the hot oil isbrought into contact with a stripping agent, such as for instancesuperheated steam w ich evaporates the light ends of the hot oil. Thestripping agent and the vaporized light ends discharge into thefractionating column.

Control of the amount of distillate taken out from the system of eachside stream'is essential since a change in this quantity affects thequality of all the heavier streams including the bottoms. It has beencustomaryto control the stream withdrawn from the main fractionatingcolumn by means of a valve in the hot liquid line betweenthefractionating and the stripping columns and then maintain the levelin the bottom of the stripping column with a liquid. level controllerwhich regulates the discharge from the stripping column. Such a control,however, is very inefiicient because the position of the valve may bechanged accidently and the valve opening often becomes obstructed bysolid or gummy material carried in the stream. I

The main object of the invention is to provide for the adjustment of astable refluxin the fractionating column by controlling the quantity ofthe side streams leaving the system through the stripping columns bymeans of a commercial rate of flow controller placed after the strippingcolumn and then causing the liquid level control on the stripping columnto operate a valve controlling the amount of oil entering from thefractionating tower into the stripping column.

The invention will be fully understood from the following descriptionread in con-' nection with theaccompanying drawing, in

which the figure is a diagrammatic side elevatien partly in section ofpreferred equipmen In the drawing, the numeral 1 denotes afractionatiiig column such as for example a bubble tower from which oneor several side streams are taken out. 2 is the line for the hot feedentering the tower, 3 for the overhead vapors, 4 for bottoms, 5 forreflux. 6, 6, 6" are the stripping columns, their number being equal tothe number of side streams. The further elements are identical on allside streams and 'will be shown only on one of them. 7 is a valved linefor the superheated ments of this type, the differential of the pressureat both sides of the orifice plate 15 controls the flow of air which inturn closes the valve 16 through the lead 17 when the differentialpressure reaches a certain fixed value. The flow in line 10 may becaused either by gravity or by a pump 18. In the latter case controlledvalve 16 in line 10 may be dispensed with and a controlled valve 19placed in the steam line of the pump 18 as marked by dotted line. Acertain portion of the cooled stripped liquid may be returned throughline 20 to provide reflux condensate.

Thepump or valve in this line'may again be do not requirefurtherdescription.

By placing the rate of flow controller after the stripping columnaccordin to the present invention and especially y placing it after thecooler, as in the preferred form of the invention, inaccuracies of therate of flow controller due to vaporization in the liquid flow to becontrolled are avoided and an accurate control of the side streamsbecomes possible. The amount of open steam ad.- mitted 'to the strippingcolumn can be easily controlled inasmuch as it is satisfactory toregulate the steam valve by hand as long as the pressure of thesuperheated steam supply is kept constant. If desired a rate of fiowcontroller may also be inserted in the steam line, or in the case of a'very light side stream closed steam coils may be used in column 6 forstripping.

Instead of returning the stripping agent and the light ends to thefractionating columnby line 9, this line may be connected by a balanceline 24 to the vapor line 3 as shown in dotted line. Since the amount ofliquid vaporized in the stripping column is small in comparison to thetotal amount of liquid passing through the same column it is stillpossible in this 'case to maintain steady reflux conditions in thefractionating column 1 by controlling the amount of side stream removedfrom the system with a rate of flow controller 12 placed behind thecooler 11.

As an example of fractionation carried out according to this invention,a Colombian lubricating distillate was heated in a pipe still andfractionated into an overhead product consisting of gas oil, a bottomsof fuel oil quality and 3 lubricating cuts taken oif the tower as sidestreams. Rate of flow controllers 12, 12, 12 were placed into the side Astreams after-the coolers 11, 11, 11" as shown on the figure and thestripping columns 6 were balanced against the vapor line 3' by means oflines 24, 24, 24. The greater part of the first side stream was returnedas reflux to the same three plates in the fractionatin column, fromwhich it was taken out. imilarly a large amount of gas oil was returnedas reflux to the top plate. The principal data of the operation aregiven in the following:

Table Amount Viscosity Baybolt Gravity sae es ie Gala/hr 8, 7

Reflux (gas oil) Reflux 1st side stream-...-

may be replaced by an receptacle adapted to contain a column 0 theliquid product removed from the system. The stripping of the side streamfrom the light ends by means of a stripping fluid such as steam istherefore not an essential part of the invention but the two constitutean advantageous combination.

Having thus described my invention and the method of carrying it out,what I claim 15:

1. In a fractionating system, a fractionatin tower, means for taking offliquid pr not from an intermediary portion of the tower, means forstripping said liquid from light ends, a line in connection with saidstripping means to remove at least part of the stripped liquid from thesystem, a, rate of flow control device in said line to regulate theamount of stripped liquid removed from the system, and a liquid levelcontrol on the strippin column to regulate the amount of liqui taken outof the fraction-' ating tower.

2. Apparatus according to claim .1 in

which a cooler is provided between the stripping means and the rate offlow control device.

"3. Apparatus according to claim 1 in which the stripping means consistsof a column and a line is provided to connect the upper part of thestripping'column to the fractionating column.

4. In a fractionatin system, a fractionatin tower, means or takingofifliquid pro uct from an intermediary portion of the tower, acontainer connected with said means and adapted to hold a column of theliquid product, a liquid discharge line connected with the container, arate of flow control device in said line to re late the amount of li uidremoved from" t e system, and a liqui level control on the container toregulate the amount of liquid taken dut of the fractionating tower.

PAUL E.

scribed with specialreference to the case I when the side stream isremoved from the fractionating tower through a stripping

